Cryogenic Gas Cooling System and Method

ABSTRACT

A pre-cool refrigeration circuit includes a pre-cool compressor configured to receive and compress pre-cool refrigerant vapor from a pre-cool heat exchanger, a pre-cool cooling device configured to receive and cool compressed pre-cool refrigerant from the pre-cool compressor, a pre-cool expansion device configured to receive and expand compressed and cooled pre-cool refrigerant from the pre-cool cooling device, and a pre-cool separation device configured to receive expanded pre-cool refrigerant from the pre-cool expansion device at a reduced pressure so as to lower a boiling point of the expanded pre-cool refrigerant and to separate the expanded pre-cool refrigerant into a pre-cool refrigerant vapor stream and a pre-cool refrigerant liquid stream. A primary refrigeration circuit includes a first primary compressor configured to receive and compress a primary refrigerant vapor from a liquefier heat exchanger and the pre-cool heat exchanger, a primary cooling device configured to receive and cool compressed primary refrigerant from the first primary compressor. The primary cooling device is in fluid communication with the pre-cool heat exchanger and the liquefier heat exchanger. A first primary expansion device is configured to receive and expand compressed and cooled primary refrigerant from the liquefier heat exchanger, with the first primary expansion device having an outlet in fluid communication with the liquefier heat exchanger and the pre-cool heat exchanger.

CLAIM OF PRIORITY

This application claims the benefit of U.S. Provisional Application No. 63/349,354, filed Jun. 6, 2022, the contents of which are hereby incorporated by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to systems and methods for refrigeration with cryogenic gases or liquefying cryogenic gases and, more particularly, to a system and method that cools cryogenic gases including a cryogenic liquid pre-cooling loop.

BACKGROUND

Industrial cryogenic gases, such as natural gas, hydrogen, neon or helium, are advantageously stored or transported in a liquid state because they occupy a much smaller volume (natural gas for instance is 1/600^(th) the gaseous state). The liquified gases are then vaporized back to a gaseous state for use at a site or system. The same cryogenic gases are also used for refrigerators, typically for research for particle accelerators, space temperature simulation, particle analysis at reduced speed (cold neutron source) or other scientific applications. Such refrigerators, however, typically boil off vaporized nitrogen to atmosphere after the liquid nitrogen is warmed to provide refrigeration and, as such, consume nitrogen.

Liquefaction of cryogenic gases is often costly. For example, gaseous hydrogen is converted to liquefied hydrogen by cooling it to about −253° C. As a result, the typical process of cooling utilizes a high amount of energy. Furthermore, the process may include multiple refrigeration cycles and involve multiple stages of gas compression.

Hydrogen liquefaction systems typically include hydrogen refrigerant cycles that use compressors. Hydrogen is difficult to compress, due to its low molecular weight and low viscosity. As a result, such compressors typically consume a large portion of the energy required to operate the system. Helium similarly is quite costly to compress. Increases in energy efficiency are desirable for cryogenic gas liquification systems and methods.

SUMMARY OF THE DISCLOSURE

There are several aspects of the present subject matter which may be embodied separately or together in the methods, devices and systems described and claimed below. These aspects may be employed alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as set forth in the claims appended hereto.

In one aspect, a system for liquefying a cryogenic gas feed stream includes a pre-cool heat exchanger including a pre-cool refrigerant warming passage, a primary refrigerant cooling passage a primary refrigerant warming passage and a feed gas cooling passage. A pre-cool refrigeration circuit includes a pre-cool compressor configured to receive and compress pre-cool refrigerant vapor from the pre-cool refrigerant warming passage of the pre-cool heat exchanger, a pre-cool cooling device configured to receive and cool compressed pre-cool refrigerant from the pre-cool compressor, a pre-cool expansion device configured to receive and expand compressed and cooled pre-cool refrigerant from the pre-cool cooling device and a pre-cool separation device configured to receive expanded pre-cool refrigerant from the pre-cool expansion device at a reduced pressure so as to lower a boiling point of the expanded pre-cool refrigerant and to separate the expanded pre-cool refrigerant into a pre-cool refrigerant vapor stream and a pre-cool refrigerant liquid stream. The pre-cool separation device has a vapor outlet and a liquid outlet in fluid communication with the pre-cool refrigerant warming passage of the pre-cool heat exchanger.

A liquefier heat exchanger includes a primary refrigerant cooling passage, a primary refrigerant warming passage and a feed gas cooling passage. A primary refrigeration circuit includes a first primary compressor configured to receive and compress a primary refrigerant vapor from the primary refrigerant warming passages of the liquefier heat exchanger and the pre-cool heat exchanger. A primary cooling device is configured to receive and cool compressed primary refrigerant from the first primary compressor, where the primary cooling device has an outlet in fluid communication with the primary refrigerant cooling passages of the pre-cool heat exchanger and the liquefier heat exchanger. A first primary expansion device is configured to receive and expand compressed and cooled primary refrigerant from the primary refrigerant cooling passage of the liquefier heat exchanger, where the first primary expansion device has an outlet in fluid communication with the primary refrigerant warming passages of the liquefier heat exchanger and the pre-cool heat exchanger.

The pre-cool heat exchanger is configured so that primary refrigerant in the primary refrigerant cooling passage of the pre-cool heat exchanger and cryogenic gas in the feed gas cooling passage are cooled by pre-cool refrigerant in the pre-cool refrigerant warming passage and primary refrigerant in the primary refrigerant warming passage. The liquefier heat exchanger is configured so that primary refrigerant in the primary refrigerant cooling passage is cooled and cryogenic fluid in the feed gas cooling passage is liquefied by primary refrigerant in the primary refrigerant warming passage.

In another aspect, a method for liquefying a cryogenic gas feed stream includes the steps of precooling the cryogenic gas feed stream using a pre-cool refrigerant and a primary refrigerant to form a pre-cooled cryogenic fluid stream and liquefying the pre-cooled cryogenic fluid stream using the primary refrigerant. A warmed pre-cool refrigerant is formed by the pre-cool step and the pre-cool and liquefaction steps form a warmed primary refrigerant. The method further includes the steps of compressing the warmed pre-cool refrigerant to form a compressed pre-cool refrigerant, cooling the compressed pre-cool refrigerant to form a cooled pre-cool refrigerant, expanding the cooled pre-cool refrigerant to form an expanded pre-cool refrigerant; reducing the pressure of the expanded pre-cool refrigerant so as to lower a boiling point of the pre-cool refrigerant, separating the pre-cool refrigerant into a pre-cool refrigerant vapor stream and a pre-cool refrigerant liquid stream, vaporizing the pre-cool refrigerant liquid stream during the pre-cooling and warming the pre-cool refrigerant vapor stream during the pre-cooling. The method further includes the steps of compressing the warmed primary refrigerant to form a compressed primary refrigerant, cooling the compressed primary refrigerant to form a cooled primary refrigerant and expanding the cooled primary refrigerant to form an expanded primary refrigerant which is warmed during the pre-cooling and liquefying steps.

The method further includes the use of a liquefied gas fed into the phase separator 136 as a pre-cool refrigerant, which is evaporated in the shown heat exchanger 46. In case of liquid nitrogen, which is typically vented to atmosphere, a vacuum pump (or ejector) 124 is required to obtain a reduced pressure.

In another aspect, a system for cooling a cryogenic gas feed stream includes a pre-cool heat exchanger including a pre-cool refrigerant warming passage, a primary refrigerant cooling passage a primary refrigerant warming passage and a feed gas cooling passage. A pre-cool refrigeration circuit includes a pre-cool compressor configured to receive and compress pre-cool refrigerant vapor from the pre-cool refrigerant warming passage of the pre-cool heat exchanger, a pre-cool cooling device configured to receive and cool compressed pre-cool refrigerant from the pre-cool compressor, a pre-cool expansion device configured to receive and expand compressed and cooled pre-cool refrigerant from the pre-cool cooling device and a pre-cool separation device configured to receive expanded pre-cool refrigerant from the pre-cool expansion device at a reduced pressure so as to lower a boiling point of the expanded pre-cool refrigerant and to separate the expanded pre-cool refrigerant into a pre-cool refrigerant vapor stream and a pre-cool refrigerant liquid stream. The pre-cool separation device has a vapor outlet and a liquid outlet in fluid communication with the pre-cool refrigerant warming passage of the pre-cool heat exchanger.

A cooling heat exchanger includes a primary refrigerant cooling passage, a primary refrigerant warming passage and a feed gas cooling passage. A primary refrigeration circuit includes a first primary compressor configured to receive and compress a primary refrigerant vapor from the primary refrigerant warming passages of the cooling heat exchanger and the pre-cool heat exchanger. A primary cooling device is configured to receive and cool compressed primary refrigerant from the first primary compressor, where the primary cooling device has an outlet in fluid communication with the primary refrigerant cooling passages of the pre-cool heat exchanger and the cooling heat exchanger. A first primary expansion device is configured to receive and expand compressed and cooled primary refrigerant from the primary refrigerant cooling passage of the cooling heat exchanger, where the first primary expansion device has an outlet in fluid communication with the primary refrigerant warming passages of the cooling heat exchanger and the pre-cool heat exchanger.

The pre-cool heat exchanger is configured so that primary refrigerant in the primary refrigerant cooling passage of the pre-cool heat exchanger and cryogenic gas in the feed gas cooling passage are cooled by pre-cool refrigerant in the pre-cool refrigerant warming passage and primary refrigerant in the primary refrigerant warming passage. The cooling heat exchanger is configured so that primary refrigerant in the primary refrigerant cooling passage is cooled and cryogenic fluid in the feed gas cooling passage is cooled by primary refrigerant in the primary refrigerant warming passage.

In another aspect, a method for cooling a cryogenic gas feed stream includes the steps of precooling the cryogenic gas feed stream using a pre-cool refrigerant and a primary refrigerant to form a pre-cooled cryogenic fluid stream and cooling the pre-cooled cryogenic fluid stream using the primary refrigerant. A warmed pre-cool refrigerant is formed by the pre-cool step and the pre-cool and liquefaction steps form a warmed primary refrigerant. The method further includes the steps of compressing the warmed pre-cool refrigerant to form a compressed pre-cool refrigerant, cooling the compressed pre-cool refrigerant to form a cooled pre-cool refrigerant, expanding the cooled pre-cool refrigerant to form an expanded pre-cool refrigerant; reducing the pressure of the expanded pre-cool refrigerant so as to lower a boiling point of the pre-cool refrigerant, separating the pre-cool refrigerant into a pre-cool refrigerant vapor stream and a pre-cool refrigerant liquid stream, vaporizing the pre-cool refrigerant liquid stream during the pre-cooling and warming the pre-cool refrigerant vapor stream during the pre-cooling. The method further includes the steps of compressing the warmed primary refrigerant to form a compressed primary refrigerant, cooling the compressed primary refrigerant to form a cooled primary refrigerant and expanding the cooled primary refrigerant to form an expanded primary refrigerant which is warmed during the pre-cooling and cooling steps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an embodiment of the cryogenic gas cooling system of the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

In accordance with embodiments of the disclosure, a cryogenic liquid refrigeration circuit provides pre-cooling of a cryogenic gas stream to reduce the energy required by a primary refrigerant compressor of a primary refrigeration circuit in liquefying or refrigerating the cryogenic gas stream. While the embodiment described below references hydrogen as both the cryogenic gas being liquefied and refrigerant of the primary refrigeration circuit and nitrogen as the cryogenic liquid of the pre-cool refrigeration circuit, alternative cryogenic gases, liquids and refrigerant compositions may be used for each. As examples only, the technology of the disclosure may be used to liquefy helium using helium or a mixture of refrigerants as the primary refrigerant and nitrogen as the pre-cool refrigerant, as described in greater detail below. Furthermore, the technology of the disclosure may alternatively be used to cool the cryogenic gas stream without liquefying it.

It should be noted herein that the lines, conduits, piping, passages and similar structures and the corresponding streams are sometimes both referred to by the same element number set out in the figures.

Also, as used herein, and as known in the art, a heat exchanger is that device or an area in the device wherein indirect heat exchange occurs between two or more streams at different temperatures, or between a stream and the environment. In addition, all heat exchangers referenced herein may be incorporated into one or more heat exchanger devices or may each be individual heat exchanger devices. As used herein, the terms “communication”, “communicating”, and the like generally refer to fluid communication unless otherwise specified. And although two fluids in communication may exchange heat upon mixing, such an exchange would not be considered to be the same as heat exchange in a heat exchanger, although such an exchange can take place in a heat exchanger.

As used herein, the terms, “high”, “middle”, “warm”, “cold” and the like are relative to comparable streams, as is customary in the art.

Reference numerals that are introduced in the specification in association with a drawing FIGURE may be repeated in one or more subsequent figures for shared elements or components without additional description in the specification in order to provide context for other features.

In the claims, letters are used to identify claimed steps (e.g. a., b. and c.). These letters are used to aid in referring to the method steps and are not intended to indicate the order in which the claimed steps are performed, unless and only to the extent that such order is specifically recited in the claims.

As illustrated in FIG. 1 , a gaseous hydrogen feed stream 8 enters a pre-cool cold box 12 and passes through passages 13 a and 13 b of pre-cool heat exchangers 14 a and 14 b, respectively where, as explained in greater detail below, it is cooled. The cooled stream then passes through one or more adsorbers 16 a and 16 b. The adsorber(s) functions to remove any type of impurity from the hydrogen fluid stream. The adsorber includes a specific material in which the impurities will be bonded to or absorbed into the material. In one embodiment, the adsorber can be comprised of a carbon, specifically an activated carbon material, but also zeolites are used.

The purified hydrogen gas stream exiting the adsorbers 16 a and 16 b then travels again through heat exchanger 14 a as a second pass where it is further cooled to approximately 80° K or less (as an example only). The cooled second pass stream then flows through heat exchanger 14 b. Passages 13 a and 13 b of heat exchangers 14 a and 14 b are refrigerated by the streams 74, 98 and 52. The heat of evaporation of the liquid in vessel 136 ensures a maximal heat removal in the first precooling cycle. Heat exchanger 14 b may contain an ortho-para conversion catalyst 18 that converts ortho-hydrogen to para-hydrogen to reduce volatilization. In the case of hydrogen liquefaction, maximal conversion of ortho to para hydrogen is achieved in this first reactor segment 18. The catalyst 18 may also be provided in heat exchanger 14 a or provided solely in heat exchanger 14 a instead.

As an example only, the pre-cool cold box 12 may be constructed with perlite with or without vacuum insulation. Alternatively, for example with smaller plant sizes, the pre-cool cold box may be integrated into the liquefier coldbox.

The pre-cooled hydrogen gas stream 22 exits the pre-cool cold box 12, at approximately 80 K (for example) in the case of traditional operation with the precool refrigerant evaporated at atmospheric pressure, and is directed to liquefier cold box 24 where it is refrigerated as a supercritical fluid in heat exchangers 26 a-26 f By evaporating the pre-cool refrigerant at a pressure below atmospheric pressure, as described in greater detail below with regard to a pre-cool separation device 136, the temperature of pre-cooled hydrogen gas stream 22 can be lowered even below 70 K. The ortho-para conversion catalyst is also provided in each of the heat exchangers 26 a-26 f for stream 22 so that ortho-para conversion is performed in parallel to the refrigeration, in order to minimize exergy losses. Since the catalytic conversion is less energy intensive at higher temperatures, it is beneficial to immediately convert all ortho-hydrogen to the thermodynamic equilibrium para hydrogen form. The liquid hydrogen product stream 32 exits the system following expansion into mixed phase flow using Joule-Thompson (JT) valve 34.

As indicated previously, the number of heat exchangers illustrated may be varied from what is shown in FIG. 1 .

Liquefier cold box 24 is insulated in order to minimize heat leaks according to the technical requirements, and preferably is vacuum insulated which may be accomplished, as an example only, via vacuum pump 36.

Cooling is provided in the liquefier cold box 24 by a primary refrigerant including hydrogen in a primary refrigeration circuit, indicated in general at 40. Cooling is provided in the pre-cool cold box 12 primarily by a pre-cool refrigerant cryogenic liquid in a pre-cool refrigeration circuit, indicated in general at 42, with supplemental cooling provided by the primary refrigerant circuit 40. In the illustrated embodiment, and as an example only, the pre-cool refrigerant used in the pre-cool refrigeration circuit 42 is nitrogen, possibly liquefied, and/or mixtures of nitrogen, carbohydrates or rare gases.

In the primary refrigeration circuit 40, a hydrogen refrigerant stream 44 enters the pre-cool cold box 12 and passes through heat exchangers 14 a and 46 where it is cooled via nitrogen (as an example only, where alternative examples are presented above) refrigerant streams 48 and 52, respectively. The cooled hydrogen fluid stream exiting heat exchanger 46 then travels through adsorber 54 and exits the pre-cool cold box 12 as stream 56. The continuously circulating refrigerant has a reduced risk of carrying/picking up contaminants. For this reason, it is possible during short periods of regeneration of the adsorber to operate the system without it.

Stream 56 enters the liquefier cold box 24 and is further cooled in heat exchanger 26 a. The hydrogen refrigerant stream exiting heat exchanger 26 a is split into streams 58 and 62.

Stream 62 is fed into an expansion device, such as expansion turbine 64, where it is expanded to a lower pressure and exits at a lower temperature as stream 65. Stream 65 is directed through heat exchanger 26 c where it is further cooled. Stream 66 exits heat exchanger 26 c and is fed into an additional expansion device, such as expansion turbine 68, where it is expanded to a lower pressure and exits at a lower temperature as stream 72. While expansion turbines 64 and 68 are illustrated in FIG. 1 , a single turbine pass or additional turbine passes, with intervening heat exchanger passes, may be used instead. In addition, alternative types of expansion devices including, but not limited to, expansion valves may be used in place of turbines 64 and 68. Furthermore, the arrangement of the expansion devices can be located at different positions and temperature levels, including, but not limited to, on stream 56 just prior to exiting pre-cool coldbox 12 and/or just after entering liquefier coldbox 24, with the goal to minimize temperature differentials in the heat exchanges for minimal exergy losses.

Valves 84 and/or 73 control the portion of stream 56 that is diverted to form stream 62, and thus ultimately refrigeration stream 72.

Stream 72 is directed through heat exchangers 26 a-26 d of the liquefier cold box to provide refrigeration therein. The warmed hydrogen stream 74 then proceeds into the pre-cool cold box 12 to provide a portion of the refrigeration within pre-cool heat exchanger 14 a. The resulting hydrogen gas stream 76 exits the pre-cool cold box 12.

Hydrogen refrigerant stream 58 travels through heat exchangers 26 a-26 e where it is further cooled. The resulting stream 78 is fed into an optional expansion turbine 80 (or other expansion device) where it is expanded to a lower pressure and exits at a lower temperature as stream 82. Stream 82 may be (further) expanded via an expansion device such as a Joule-Thomson valve 84, with the resulting mixed phase stream 86 directed to primary refrigerant separation device 88.

A liquid hydrogen refrigerant stream 92 exits the bottom of primary refrigerant separation device 88 and is directed through liquefier evaporator 26 f of the liquefier cold box to provide refrigeration therein. The heat of evaporation is used for the final cool-down step and ortho-para conversion for the hydrogen feed gas stream. The JT-expansion valve 34 can also or alternatively be positioned between 26 e and 26 f heat exchangers. It may also be executed as an ejector.

A hydrogen refrigerant vapor stream 94 exits the top of the primary refrigerant separation device 88 and is combined with stream 92 to form combined hydrogen refrigerant stream 96, which is directed through liquefier heat exchangers 26 e-26 a to provide refrigeration therein. A resulting warmed hydrogen refrigerant stream 98 exits the liquefier cold box 24.

Streams 72 and 96 cooperate to provide the refrigeration required to liquefy pre-cooled hydrogen stream 22 in the liquefier cold box 24. For example, the temperature of the hydrogen gas stream 22 may be reduced to approximately 20° K-22° K in the cold end of the liquefier cold box 24.

Stream 98 flows into the pre-cool cold box 12 to provide a portion of the refrigeration within heat exchanger 14 a. The resulting hydrogen gas stream 102 exits the pre-cool cold box 12.

Hydrogen refrigerant vapor stream 102 travels to a first primary compressor 104 of the primary refrigeration circuit and is pressurized to form medium pressure vapor stream 106. Hydrogen refrigerant vapor stream 76 joins medium pressure vapor stream 106 to form combined hydrogen refrigerant vapor stream 108, which is pressurized in second primary compressor 112 to form high pressure vapor stream 114. Stream 102 requires the additional compression/pressurization provided by compressor 104 to compensate for the additional pressure drops experienced by stream 58 as it travels through the additional heat exchangers of the liquefier cold box 24, turbine 80, JT valve 84 and separation device 88.

In some embodiments, the pressure in vessel 88 may be minimized to have the lowest possible temperature of evaporation. For this reason, in such an embodiment and as an example only, the small partial stream 82 is boiling in the 20 K range providing a heat sink to the 1.3-1.5 bara operated liquefier.

High pressure vapor stream 114 is directed through a primary cooling device, such as heat exchanger 116, where it is cooled by direct/indirect heat exchange with water stream 118 and/or air coolers in locations with lack of enough cooling water. As a result, hydrogen refrigerant stream 44 is formed. Alternative cooling fluids including, but not limited to, ambient air, may be used in place of water 118.

In the pre-cool refrigeration circuit 42, nitrogen refrigerant vapor 122 enters pre-cool compressor 124. The resulting compressed stream is cooled in a pre-cool cooling device, such as heat exchanger 126, by indirect heat exchange with water stream 128. Alternative cooling fluids including, but not limited to, ambient air, may be used in place of water stream 128. The resulting cooled nitrogen vapor stream is expanded in a pre-cool expansion device, such as expansion turbine 132 and/or a combination of expansion turbines and compressors. The resulting mixed phase nitrogen stream 134 is directed to pre-cool refrigeration circuit separation device 136.

Different setups for compressor/heat exchangers as known from the air separation industry are to be foreseen in the precooling section, including but not limited to an expansion of the compressed nitrogen in a JT-valve into the vessel 136, where only a portion of the stream 134 enters. The remaining stream may pass via expansion turbines/companders run through heat exchanger 52.

Pre-cool refrigeration circuit separation device 136 preferably is operated at a reduced pressure to lower the boiling temperature of entering pre-cool refrigerant stream 134. As example only, when nitrogen is used as the pre-cool liquid refrigerant, the pressure within the separation device 136 may be 0.5 bar so as to lower the boiling temperature of the nitrogen in the separation device from 78 K to 73 K. Indeed, as alternatives to nitrogen, any pre-cooling refrigerant which allows an operation at a temperature lower than 77 K, will improve the overall process efficiency.

A liquid nitrogen refrigerant stream 52 exits the pre-cool refrigeration circuit separation device 136 and, as described previously, provides cooling in heat exchanger 46. An overhead vapor stream 138 exits the separation deice 136 and joins the nitrogen stream exiting the heat exchanger 46. The resulting combined nitrogen refrigerant stream 48 flows through heat exchanger 14 a and provides refrigeration therein so that nitrogen refrigerant vapor stream 122 is produced. In alternative embodiments, the separation device 136 may be omitted so that streams 52 and 48 are formed directly from stream 134.

The compressors 104 and 112 of the primary refrigeration circuit 40 of FIG. 1 require more energy to operate than the compressor 124 of the pre-cool refrigeration circuit 42. In addition, the pre-cool refrigeration circuit 42 reduces the cooling requirements, and thus compression requirements, of the primary refrigeration circuit 40. As a result, the embodiment of FIG. 1 effectively permits a portion of the cooling power of the system to be shifted from the primary refrigeration circuit 40 to the pre-cool refrigeration circuit 42 so that the overall energy usage and power requirements of the system, and thus the liquefaction of the hydrogen gas feed stream, are reduced (The Carnot cycle process at elevated temperature requires less energy).

In an alternative embodiment of the system of the disclosure, the system of FIG. 1 may be re-configured to liquefy helium gas by removal of heat exchangers 26 e and 26 f and the addition of an expansion device, such as a JT valve, downstream of heat exchanger 26 d. As a result, in such a system, stream 58 will be expanded in the JT valve after having passed through heat exchangers 26 a-26 d. As an example only, in such a system, helium could be the refrigerant of the primary refrigeration circuit and nitrogen could be the cryogenic liquid of the pre-cool refrigeration circuit.

While the preferred embodiments of the disclosure have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the disclosure, the scope of which is defined by the following claims. 

What is claimed is:
 1. A system for liquefying a cryogenic gas feed stream comprising: a. a pre-cool heat exchanger including a pre-cool refrigerant warming passage, a primary refrigerant cooling passage a primary refrigerant warming passage and a feed gas cooling passage; b. a pre-cool refrigeration circuit including: i) a pre-cool compressor configured to receive and compress pre-cool refrigerant vapor from the pre-cool refrigerant warming passage of the pre-cool heat exchanger; ii) a pre-cool cooling device configured to receive and cool compressed pre-cool refrigerant from the pre-cool compressor; iii) a pre-cool expansion device configured to receive and expand compressed and cooled pre-cool refrigerant from the pre-cool cooling device; iv) a pre-cool separation device configured to receive expanded pre-cool refrigerant from the pre-cool expansion device at a reduced pressure so as to lower a boiling point of the expanded pre-cool refrigerant and to separate the expanded pre-cool refrigerant into a pre-cool refrigerant vapor stream and a pre-cool refrigerant liquid stream, said pre-cool separation device having a vapor outlet and a liquid outlet in fluid communication with the pre-cool refrigerant warming passage of the pre-cool heat exchanger; c. a liquefier heat exchanger including a primary refrigerant cooling passage, primary refrigerant warming passage and a feed gas cooling passage; d. a primary refrigeration circuit including: i) a first primary compressor configured to receive and compress a primary refrigerant vapor from the primary refrigerant warming passages of the liquefier heat exchanger and the pre-cool heat exchanger; ii) a primary cooling device configured to receive and cool compressed primary refrigerant from the first primary compressor, said primary cooling device having an outlet in fluid communication with the primary refrigerant cooling passages of the pre-cool heat exchanger and the liquefier heat exchanger; iii) a first primary expansion device configured to receive and expand compressed and cooled primary refrigerant from the primary refrigerant cooling passage of the liquefier heat exchanger, said first primary expansion device having an outlet in fluid communication with the primary refrigerant warming passages of the liquefier heat exchanger and the pre-cool heat exchanger; e. said pre-cool heat exchanger configured so that primary refrigerant in the primary refrigerant cooling passage of the pre-cool heat exchanger and cryogenic gas in the feed gas cooling passage are cooled by pre-cool refrigerant in the pre-cool refrigerant warming passage and primary refrigerant in the primary refrigerant warming passage; and f. said liquefier heat exchanger configured so that primary refrigerant in the primary refrigerant cooling passage is cooled and cryogenic fluid in the feed gas cooling passage is liquefied by primary refrigerant in the primary refrigerant warming passage.
 2. The system of claim 1, further comprising pre-cool cold box within which the pre-cool heat exchanger is positioned and a liquefier cold box within which the liquefier heat exchanger is positioned.
 3. The system of claim 2 wherein the liquefier heat exchanger is vacuum insulated.
 4. The system of claim 1 wherein the first primary expansion device is a Joule-Thompson valve.
 5. The system of claim 1 wherein the liquefaction heat exchanger includes a first liquefaction heat exchanger having a first primary refrigerant cooling passage, a first primary refrigerant warming passage and a second primary refrigerant warming passage, said liquefaction heat exchanger also including a second liquefaction heat exchanger having a second primary refrigerant cooling passage, a third primary refrigerant cooling passage, a third primary refrigerant warming passage and a fourth primary refrigerant warming passage and further comprising; g. a split configured to receive primary refrigerant exiting the first primary refrigerant passage cooling passage; h. a second primary expansion device configured to receive a first portion of primary refrigerant from the split, said second primary expansion device having a second primary expansion device outlet; i. said second primary refrigerant cooling passage of the second heat exchanger configured to receive and cool the first portion of primary refrigerant from the second primary expansion device outlet, said second primary refrigerant cooling passage in fluid communication with the third and first primary refrigerant warming passages; j. said third primary refrigerant cooling passage of the second heat exchanger configured to receive and cool a second portion of primary refrigerant from the split, said third primary refrigerant cooling passage in fluid communication with the fourth and second primary refrigerant warming passages.
 6. The system of claim 5 wherein the second primary expansion device is a turbine.
 7. The system of claim 5 further comprising a third primary expansion device configured to receive the first portion of primary refrigerant from the second primary refrigerant cooling passage of the second liquefaction heat exchanger, said third primary expansion device having a third primary expansion device outlet wherein said third and first primary refrigeration passages are configured to receive the first portion of primary refrigerant from the third primary expansion device outlet.
 8. The system of claim 7 wherein the second and third expansion devices are turbines.
 9. The system of claim 5 wherein the first primary compressor has a first primary compressor inlet configured to receive the second portion of primary refrigerant from the second primary refrigerant warming passage of the first heat exchanger and further comprising a second primary compressor having a primary compressor inlet configured to receive primary refrigerant from the first primary refrigerant warming passage and primary refrigerant from the first primary compressor.
 10. The system of claim 1 wherein the cryogenic gas feed stream includes hydrogen, the primary refrigerant includes hydrogen and the pre-cool refrigerant includes nitrogen.
 11. The system of claim 1 wherein the pre-cool refrigerant is nitrogen and the pressure within the pre-cool separation device is reduced to approximately 0.5 bar to lower a boiling temperature of the nitrogen from 78 K to approximately 73 K.
 12. The system of claim 1 wherein the pressure within the pre-cool separation device is reduced to a level whereby a boiling temperature of the pre-cool refrigerant is below 77 K.
 13. A method for liquefying a cryogenic gas feed stream comprising the steps of: a. precooling the cryogenic gas feed stream using a pre-cool refrigerant and a primary refrigerant to form a pre-cooled cryogenic fluid stream; b. liquefying the pre-cooled cryogenic fluid stream using the primary refrigerant; c. wherein step a. forms a warmed pre-cool refrigerant and steps a. and b. form a warmed primary refrigerant; d. compressing the warmed pre-cool refrigerant to form a compressed pre-cool refrigerant; e. cooling the compressed pre-cool refrigerant to form a cooled pre-cool refrigerant; f. expanding the cooled pre-cool refrigerant to form an expanded pre-cool refrigerant; g. reducing the pressure of the expanded pre-cool refrigerant so as to lower a boiling point of the pre-cool refrigerant; h. separating the pre-cool refrigerant of step g. into a pre-cool refrigerant vapor stream and a pre-cool refrigerant liquid stream; i. vaporizing the pre-cool refrigerant liquid stream during the pre-cooling of step a.; j. warming the pre-cool refrigerant vapor stream during the pre-cooling of step a.; k. compressing the warmed primary refrigerant to form a compressed primary refrigerant; l. cooling the compressed primary refrigerant to form a cooled primary refrigerant; m. expanding the cooled primary refrigerant to form an expanded primary refrigerant which is warmed during the pre-cooling of step a. and the liquefying of step b.
 14. The method of claim 13 wherein the cryogenic gas feed stream includes hydrogen, pre-cool refrigerant includes nitrogen and the primary refrigerant includes hydrogen.
 15. The method of claim 13 wherein the cooling of steps e. and h. are performed using water.
 16. The method of claim 13 wherein the cooling of step h. includes cooling by the pre-cool refrigerant.
 17. The method of claim 13 wherein the pre-cool refrigerant is nitrogen and the pressure within the pre-cool separation device is reduced in step g. to approximately 0.5 bar to lower a boiling temperature of the nitrogen from 78 K to approximately 73 K.
 18. The method of claim 13 wherein the pressure within the pre-cool separation device is reduced in step g. to a level whereby a boiling temperature of the pre-cool refrigerant is below 77 K.
 19. A system for cooling a cryogenic gas feed stream comprising: a. a pre-cool heat exchanger including a pre-cool refrigerant warming passage, a primary refrigerant cooling passage a primary refrigerant warming passage and a feed gas cooling passage; b. a pre-cool refrigeration circuit including: i) a pre-cool compressor configured to receive and compress pre-cool refrigerant vapor from the pre-cool refrigerant warming passage of the pre-cool heat exchanger; ii) a pre-cool cooling device configured to receive and cool compressed pre-cool refrigerant from the pre-cool compressor; iii) a pre-cool expansion device configured to receive and expand compressed and cooled pre-cool refrigerant from the pre-cool cooling device; iv) a pre-cool separation device configured to receive expanded pre-cool refrigerant from the pre-cool expansion device at a reduced pressure so as to lower a boiling point of the expanded pre-cool refrigerant and to separate the expanded pre-cool refrigerant into a pre-cool refrigerant vapor stream and a pre-cool refrigerant liquid stream, said pre-cool separation device having a vapor outlet and a liquid outlet in fluid communication with the pre-cool refrigerant warming passage of the pre-cool heat exchanger; c. a cooling heat exchanger including a primary refrigerant cooling passage, primary refrigerant warming passage and a feed gas cooling passage; d. a primary refrigeration circuit including: i) a first primary compressor configured to receive and compress a primary refrigerant vapor from the primary refrigerant warming passages of the cooling heat exchanger and the pre-cool heat exchanger; ii) a primary cooling device configured to receive and cool compressed primary refrigerant from the first primary compressor, said primary cooling device having an outlet in fluid communication with the primary refrigerant cooling passages of the pre-cool heat exchanger and the cooling heat exchanger; iii) a first primary expansion device configured to receive and expand compressed and cooled primary refrigerant from the primary refrigerant cooling passage of the cooling heat exchanger, said first primary expansion device having an outlet in fluid communication with the primary refrigerant warming passages of the cooling heat exchanger and the pre-cool heat exchanger; e. said pre-cool heat exchanger configured so that primary refrigerant in the primary refrigerant cooling passage of the pre-cool heat exchanger and cryogenic gas in the feed gas cooling passage are cooled by pre-cool refrigerant in the pre-cool refrigerant warming passage and primary refrigerant in the primary refrigerant warming passage; and f. said cooling heat exchanger configured so that primary refrigerant in the primary refrigerant cooling passage is cooled and cryogenic fluid in the feed gas cooling passage is cooled by primary refrigerant in the primary refrigerant warming passage.
 20. A method for cooling a cryogenic gas feed stream comprising the steps of: a. precooling the cryogenic gas feed stream using a pre-cool refrigerant and a primary refrigerant to form a pre-cooled cryogenic fluid stream; b. cooling the pre-cooled cryogenic fluid stream using the primary refrigerant; c. wherein step a. forms a warmed pre-cool refrigerant and steps a. and b. form a warmed primary refrigerant; d. compressing the warmed pre-cool refrigerant to form a compressed pre-cool refrigerant; e. cooling the compressed pre-cool refrigerant to form a cooled pre-cool refrigerant; f. expanding the cooled pre-cool refrigerant to form an expanded pre-cool refrigerant; g. reducing the pressure of the expanded pre-cool refrigerant so as to lower a boiling point of the pre-cool refrigerant; h. separating the pre-cool refrigerant of step g. into a pre-cool refrigerant vapor stream and a pre-cool refrigerant liquid stream; i. vaporizing the pre-cool refrigerant liquid stream during the pre-cooling of step a.; j. warming the pre-cool refrigerant vapor stream during the pre-cooling of step a.; k. compressing the warmed primary refrigerant to form a compressed primary refrigerant; l. cooling the compressed primary refrigerant to form a cooled primary refrigerant; m. expanding the cooled primary refrigerant to form an expanded primary refrigerant which is warmed during the pre-cooling of step a. and the cooling of step b. 